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PubMed1998

Stability of microsatellites in myeloid neoplasias.

Microsatellites are short, repeated DNA sequences that exist throughout the genome. Instability of these sequences, associated with defects in the DNA mismatch repair system, is the hallmark of hereditary non-polyposis colorectal cancer (HNPCC), and is also found in many sporadic cancers. Although many types of solid tumors exhibit this type of genetic instability, its involvement in hematologic cancers is less evident. We have investigated whether microstatellite instability (MSI) is involved in the transformation of myeloid cells to myelodysplastic syndrome (MDS) and/or acute myelogenous leukemia (AML). Both de novo and treatment-associated neoplasias were studied. Only one example of MSI was found in 48 patients, using a panel of 14 different microsatellite loci consisting of repeats of one to four base pairs. These results suggest that the genes responsible for MSI are not involved in the transformation of normal myeloid cells to MDS or AML.

Chromosome Aberrations↗
PubMed1999

MSH3 deficiency is not sufficient for a mutator phenotype in Chinese hamster ovary cells.

In the yeast Saccharomyces cerevisiae, the mutS homolog protein products MSH3 and MSH6, each in cooperation with MSH2, play well-defined and specific roles in the repair of DNA mismatches and nucleotide loops. The discrete functions of the human homologs hMSH3 and hMSH6 are less clear and current evidence suggests that the substrate specificity of these proteins may be less strict. To determine the role of MSH3 in mammalian mismatch repair, we employed MSH3-deficient Chinese hamster ovary (CHO) cell lines. No significant changes in mutation rate were detected in the MSH3-deficient strain and there were no differences in sensitivity to DNA-damaging agents. Further analysis of hprt mutants did not show a MSH3-dependent shift in the mutant spectrum. Interestingly, thorough examination of four dinucleotide microsatellite regions revealed instability at only one locus in one of the MSH3-deficient cell lines. These data support the idea of a high degree of redundancy in the function of the MutS homologs MSH3 and MSH6, at least with respect to the control of microsatellite instability.

Animals↗
PubMed2001

Mismatch repair in correction of replication errors and processing of DNA damage.

The primary role of mismatch repair (MMR) is to maintain genomic stability by removing replication errors from DNA. This repair pathway was originally implicated in human cancer through an association between microsatellite instability in colorectal tumors in hereditary nonpolyposis colon cancer (HNPCC) kindreds. Microsatellites are short repetitive sequences which are often copied incorrectly by DNA polymerases because the template and daughter strands in these regions are particularly prone to misalignment. These replication-dependent events create loops of extrahelical bases which would produce frameshift mutations unless reversed by MMR. One consequence of MMR loss is a widespread expansion and contraction of these repeated sequences that affects the whole genome. Defective MMR is therefore associated with a mutator phenotype. Since the same pathway is also responsible for repairing base:base mismatches, defective cells also experience large increases in the frequency of spontaneous transition and transversion mutations. Three different approaches have been used to investigate the function of individual components of the MMR pathway. The first is based on the biochemical characterization of the purified protein complexes using synthetic DNA substrates containing loops or single mismatches. In the second, the biological consequences of MMR loss are inferred from the phenotype of cell lines established from repair-deficient human tumors, from tolerant cells or from mice defective in single MMR genes. In particular, molecular analysis of the mutations in endogenous or reporter genes helped to identify the DNA substrates for MMR. Finally, mice bearing single inactive MMR genes have helped to define the involvement of MMR in cancer prevention.

Animals↗
PubMed2003

[Mismatch pair defective phenotype in hereditary nonpolyposis colorectal cancer in the Chinese].

OBJECTIVE: To study the protein expression pattern of DNA mismatch repair genes hMSH(2), hMLH(1) and the microsatellite instability (MSI) status in the tumor tissue from hereditary nonpolyposis colorectal cancer in the Chinese. METHODS: Fifty-eight families fulfilling different clinical criteria including Amsterdam Criteria (AC) (22/24 families, 38 tumors), Japanese Criteria (JC) (12/15 families, 16 tumors) and Bethesda Guidelines (BG) (12/19 patients, 13 tumors) were studied. Monoclonal antibodies against hMSH(2), hMLH(1) proteins and a panel of microsatellite markers (5 loci) including BAT26, BAT25, D2S123, D5S346 and D17S250 were used for study. RESULTS: MSI-H was identified in all 22 (100%) AC tumors, with 81.8% (18/22) showing altered hMSH(2) or hMLH(1) expression; in 14/15 (93.8%) JC cancer, 1/1 (100%) JC adenoma, with 45.5% (5/11) showing altered hMSH(2) or hMLH(1) expression; and in 7/13 (53.8%) BG tumors, with 4/7 showing loss of hMSH(2) or hMLH(1) gene expression. CONCLUSION: The frequency of MSI-H and loss of mismatch repair protein are different in the families fulfilling different clinical criteria. Amsterdam Criteria and Japanese Criteria are the two most useful criterion systems for identifying mismatched repair defective tumors. However, Bethesda Guidelines should also be used for detecting more such tumors. The combination of immunohistochemical methods and microsatellite instability analysis is an effective strategy to detect the mismatch repair defective tumors. A close correlation does exist between hMSH(2), hMLH(1) protein expression pattern and MSI status.

Adaptor Proteins, Signal Transducing↗
PubMed2001

Bethesda guidelines: relation to microsatellite instability and MLH1 promoter methylation in patients with colorectal cancer.

BACKGROUND: Microsatellite instability is a hallmark of mismatch repair deficiency in hereditary nonpolyposis colorectal cancer and results from mutations in the mismatch repair genes MLH1 or MSH2 or from gene inactivation associated with DNA methylation. The Bethesda guidelines were established to identify patients with colorectal cancer who should be tested for microsatellite instability. OBJECTIVE: To assess the Bethesda guidelines for detection of microsatellite instability and to determine the role of MLH1 promoter methylation in colorectal cancer. DESIGN: Prospective cohort study. SETTING: Tertiary care referral center in Frankfurt, Germany. PATIENTS: 125 consecutive patients with colorectal cancer. MEASUREMENTS: Patients were assessed according to the Bethesda guidelines, and tumor specimens were analyzed for microsatellite instability. Patients with microsatellite instability were tested for MLH1 promoter methylation and MLH1 and MSH2 germline mutations. RESULTS: Microsatellite instability was detected in 17 of 58 patients who fulfilled and 5 of 67 patients who did not fulfill criteria of the Bethesda guidelines. In 11 of 17 patients with microsatellite instability who fulfilled Bethesda guidelines, an MLH1 (n = 3), MSH2 (n = 7), or combined MLH1 and MSH2 (n = 1) mutation was found. Among the patients with microsatellite instability who did not fulfill Bethesda guidelines, no mutations were observed; MLH1 promoter methylation was observed in 6 of 11 patients with an MLH1 or MSH2 mutation and 5 of 11 patients without an MLH1 or MSH2 mutation. CONCLUSIONS: The Bethesda guidelines are useful for selecting patients for microsatellite instability testing. MLH1 and MSH2 testing should be recommended in all patients with colorectal cancer and microsatellite instability who fulfill at least one Bethesda criterion. MLH1 promoter methylation may accompany rather than initiate carcinogenesis in patients with colorectal cancer who have mismatch repair gene defects.

Adaptor Proteins, Signal Transducing↗
PubMed1996

Microsatellite instability and mutation analysis of hMSH2 and hMLH1 in patients with sporadic, familial and hereditary colorectal cancer.

To date, at least four genes involved in DNA mismatch repair, hMSH2, hMLH1, hPMS1 and hPMS2, have been demonstrated to be altered in the germline of patients with hereditary nonpolyposis colorectal cancer (HNPCC). Additionally, defective mismatch repair is thought to account for the observation of microsatellite instability (MIN) in tumors from these patients. The genetic defect responsible for the MIN+ phenotype in sporadic colorectal cancer, however, has yet to be clearly delineated. In order to better understand the role of somatic and germline alterations within hMSH2 and hMLH1 in the process of colorectal tumorigenesis, we examined the entire coding regions of both of these genes in seven patients with MIN+ sporadic colorectal cancer, 19 patients with familial colorectal cancer, and 20 patients meeting the strict Amsterdam criteria for HNPCC. Thirteen germline, two somatic, and four neutral alterations were identified. The two somatic mutations occurred in patients having familial cancer, while the germline mutations were distributed among one sporadic (14%), three familial (16%), and nine HNPCC (45%) cases. All patients with identified mutations in the mismatch repair genes, whose tumors were available for analysis, demonstrated MIN. On the other hand, we could not identify mutations in the subset of clinically defined HNPCC patients with MIN negative tumors nor in the majority (6/7) of MIN+ sporadic tumors.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Pedigree and genetic analysis of a novel mutation carrier patient suffering from hereditary nonpolyposis colorectal cancer.

AIM: To screen a suspected Hungarian HNPCC family to find specific mutations and to evaluate their effect on the presentation of the disease. METHODS: The family was identified by applying the Amsterdam and Bethesda Criteria. Immunohistochemistry was performed, and DNA samples isolated from tumor tissue were evaluated for microsatellite instability. The identification of possible mutations was carried out by sequencing the hMLH1 and hMSH2 genes. RESULTS: Two different mutations were observed in the index patient and in his family members. The first mutation was located in exon 7, codon 422 of hMSH2, and caused a change from Glu to STOP codon. No other report of such a mutation has been published, as far as we could find in the international databases. The second mutation was found in exon 3 codon 127 of the hMSH2 gene, resulting in Asp-->Ser substitution. The second mutation was already published, as a non-pathogenic allelic variation. CONCLUSION: The pedigree analysis suggested that the newly detected nonsense mutation in exon 7 of the hMSH2 gene might be responsible for the development of colon cancers. In family members where the exon 7 mutation is not coupled with this missense mutation, colon cancer appears after the age of 40. The association of these two mutations seems to decrease the age of manifestation of the disease into the early thirties.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Epigenetic lesions causing genetic lesions in human cancer: promoter hypermethylation of DNA repair genes.

The existence of genetic alterations affecting genes involved in cellular proliferation and death, such as TP53 and K-ras, is one of the most common features of tumour cells. Recently, gene inactivation by promoter hypermethylation has been demonstrated. Methylation is the main epigenetic modification in mammals and abnormal methylation of the CpG islands located in the promoter region of the genes leads to transcriptional silencing. Examples include the p16INK4a, p15INK4B, p14ARF, Von Hippel-Lindau (VHL), the oestrogen and progesterone receptors, E-cadherin, death associated protein (DAP) kinase and the first tumour suppressor gene described, retinoblastoma (Rb) gene. In most cases, methylation involves loss of expression, absence of a coding mutation and restoration of transcription by the use of demethylating agents. However, is there a linkage between genetic and epigenetic alterations? Our results show one side of this puzzle demonstrating that epigenetic lesions drive genetic lesions in cancer. Four specific epigenetic lesions, promoter hypermethylation of the DNA mismatch repair gene hMLH1, the DNA alkyl-repair gene O(6)-methylguanine-DNA methyltransferase (MGMT), the detoxifier glutathione S-transferase P1 (GSTP1) and the familial breast cancer gene BRCA1 may lead to four specific genetic lesions, microsatellite instability, G to A transitions, steroid-related adducts and double-strand breaks in DNA. This is probably only the beginning of an extensive list of epigenetic events that change and make the genetic environment of the transformed cell unstable.

DNA Methylation↗
PubMed1999

Two case studies of chronic idiopathic neutropenia preceding acute myeloid leukaemia.

Chronic idiopathic neutropenia is regarded as a benign disorder without risk of malignant transformation. We present two patients with chronic idiopathic neutropenia who showed disease progression to acute myeloid leukaemia. Sequence analysis of the granulocyte-colony stimulating factor receptor (G-CSFR) gene from leukaemic DNA did not reveal any mutations and microsatellite analysis provided no evidence of microsatellite instability or loss of constitutional heterozygosity. These case studies suggest that chronic idiopathic neutropenia may constitute a preleukaemic condition in some patients. Alterations of the G-CSFR or defective DNA mismatch repair do not appear to be involved in malignant transformation.

Acute Disease↗
PubMed2001

"Second hit" in sebaceous tumors from Muir-Torre patients with germline mutations in MSH2: allele loss is not the preferred mode of inactivation.

Muir-Torre syndrome is an autosomal-dominant inherited disorder predisposing to both sebaceous skin tumors and internal neoplasms. In a significant proportion of Muir-Torre syndrome patients skin tumors exhibit microsatellite instability as a hallmark of hereditary nonpolyposis colorectal cancer. Most individuals predisposed to hereditary nonpolyposis colorectal cancer harbor a germline mutation in the DNA mismatch repair genes MSH2 or MLH1. In Muir-Torre syndrome the vast majority of germline mutations have been identified in MSH2. Microsatellite instability in tumor tissue develops after somatic inactivation of the corresponding second mismatch repair allele ("second hit"). So far, the mechanisms of somatic inactivation of the second allele in microsatellite instability positive tumors from patients with known mismatch repair germline mutations are not well understood. We examined whether allele loss (loss of heterozygosity) is a frequent mechanism for inactivation of the second MSH2 allele in a sample of nine microsatellite instability positive skin tumors from eight unrelated Muir-Torre patients with known MSH2 germline mutations. Loss of heterozygosity was determined using microsatellite markers or heteroduplex analysis, respectively. Only one of the nine skin tumors exhibited loss of heterozygosity at the MSH2 locus. Thus, we could show in a sample of sebaceous tumors from patients with genetically proven Muir-Torre syndrome that loss of heterozygosity most probably is not the preferred mode of somatic inactivation of the second MSH2 allele.

Adult↗
PubMed2006

Immunohistochemical investigation of tumorigenic pathways in small intestinal adenocarcinoma: a comparison with colorectal adenocarcinoma.

Small intestinal adenocarcinoma is an uncommon neoplasm morphologically similar to or indistinguishable from colorectal adenocarcinoma. Although much has been learned about genetic pathways critical to colorectal tumorigenesis, little is known about molecular alterations involved in the development of small intestinal adenocarcinoma. In this study, we immunohistochemically compared non-ampullary small intestinal adenocarcinomas with sporadic colorectal adenocarcinomas for the expression of several proteins known to serve pivotal roles in colorectal tumorigenesis. These included adenomatous polyposis coli and beta-catenin involved in the Wnt signaling pathway, and DNA mismatch repair enzymes hMLH1, hMSH2 and hMSH6 involved in the microsatellite instability pathway. The expression of two important tumor suppressors, p53 and RB, was also examined. The results show that complete loss of adenomatous polyposis coli immunoreactivity, presumably resulting from its gene mutations, was observed in eight of 26 (31%) small intestinal adenocarcinomas and 36 of 51 (71%) colorectal adenocarcinomas (P = 0.0008). Nuclear localization of beta-catenin, an indirect evidence of deregulated Wnt signaling pathway, was observed in 5 (19%) small intestinal adenocarcinomas and 36 (71%) colorectal adenocarcinomas (P<0.0001). Total lack of nuclear staining for one or more of the DNA mismatch repair enzymes occurred in a similar low frequency in both small intestinal and colorectal adenocarcinomas, seen in two of 25 (8%) and 10 of 47 (21%) cases, respectively (P = 0.1958). The frequencies of aberrant p53 and RB expression were also similar between small intestinal and colorectal adenocarcinomas. These observations indicate that defects in the Wnt and microsatellite instability pathways occur in over 90% of colorectal adenocarcinomas, but in only 40% of small intestinal adenocarcinomas. Small intestinal tumorigenesis appears to follow a distinct, yet unidentified, molecular pathway(s) from its colorectal counterpart despite their morphologic similarity.

Adaptor Proteins, Signal Transducing↗
PubMed2002

Inactivation of O6-methylguanine-DNA methyltransferase by promoter CpG island hypermethylation in gastric cancers.

Promoter hypermethylation of CpG islands in tumour suppressor genes can lead to transcriptional inactivation. To investigate the association between methylation and expression at O6-methylguanine-DNA methyltransferase, we performed methylation-specific PCR and immunohistochemistry in 149 gastric carcinomas. Promoter methylation was found in 14.1% of tumours and loss of expression was detected in 11.4% of tumours. To examine correlation between the O6-methylguanine-DNA methyltransferase expression and the clinical data, we investigated O6-methylguanine-DNA methyltransferase expression in 315 consecutive gastric carcinomas. A similar frequency of loss of O6-methylguanine-DNA methyltransferase expression was confirmed in these cases. The loss of O6-methylguanine-DNA methyltransferase expression was significantly associated with pTNM stage (P=0.037), tumour invasion (P=0.02), microsatellite instability (P=0.041) and overall survival (P=0.01). Among 11 gastric cancer cell lines, SNU-620 showed the loss of O6-methylguanine-DNA methyltransferase expression as well as promoter methylation. After treatment with 5-aza-2-deoxycytidine, a demethylating agent, SNU-620 re-expressed O6-methylguanine-DNA methyltransferase mRNA. In summary, we suggest that during gastric carcinogenesis, the loss of O6-methylguanine-DNA methyltransferase expression frequently occurs via the hypermethylation of the CpG islands of the promoter region, and that this is significantly associated with the clinicopathological characteristics.

Antimetabolites, Antineoplastic↗
PubMed2006

Contribution of microdissection for the detection of microsatellite instability in colorectal cancer.

The determination ofmicrosatellite instability (MSI) is an important step in the identification of familial colorectal cancer such as hereditary nonpolyposis colon cancer. It could also be of interest in the therapeutic management of sporadic cancer. International criteria for the determination of MSI have been published, recommending the use of microdissection. The aim of this work was to evaluate the impact of contaminant normal DNA in tumor samples for MSI assessment in colorectal cancer using a microdissection technique. We performed a comparative analysis of the microsatellite status between total DNA (DNA extracted from whole tumor samples) and microdissected DNA in 3 different regions from 23 cases of colorectal cancer. Six microsatellites were amplified using fluorescent polymerase chain reaction. We analyzed 9 cases with MSI and 14 cases without instability, with similar results between total DNA and microdissected DNA. Moreover, within a same tumor, the MSI phenotype was observed regardless of the region analyzed. Thus, this work shows the reproducibility of the MSI phenotype throughout a tumor. However, we observed a regional heterogeneity of the MSI profile, consisting of variations in the number and the size of unstable alleles within different regions. This result reflects the genetic heterogeneity of colorectal cancer with MSI. In the 14 cases without instability, we observed an increase of more than 60% in the loss of heterozygosity detection rate after microdissection. Thus, this work confirms the contribution of microdissection for loss of heterozygosity assessment.

Adenocarcinoma↗
PubMed2005

Detecting mismatch repair defects in myeloma.

Defects in the mismatch repair system are associated with a microsatellite unstable phenotype. In this chapter, we describe the preparation of purified plasma cells using CD138 magnetic microbeads as a source of tumor DNA. We also describe a robust, sensitive method for comparing microsatellite repeat units of tumor to constitutive DNA using polymerase chain reaction and laser scanning of fluorescently labeled amplicons in an automated sequencer in order to assess microsatellite instability in myeloma.

Antigens, CD↗
PubMed2000

Atypical clustering of gynecologic malignancies: A family study including molecular analysis of candidate genes.

OBJECTIVE: We set out to determine whether hereditary nonpolyposis colorectal cancer (HNPCC) was responsible for cancer susceptibility in a family with gynecologic malignancies in three consecutive generations. METHODS: A detailed family history study, including review of medical records, was undertaken. Tumor DNAs from affected family members were evaluated for microsatellite instability (MSI). Linkage between cancer susceptibility and the candidate DNA mismatch repair genes MLH1, MSH2, MSH3, and MSH6 (GTBP) was investigated. MLH1 and MSH2 protein expression was evaluated by immunohistochemistry and MSH2 was investigated for mutation. RESULTS: Four gynecologic malignancies in the core family were confirmed. MSI was seen in six of seven cancers studied. The only MSI-negative tumor was an ovarian cancer from the proband's maternal grandmother, which arose at the age of 92. Haplotype analysis using chromosome 2p markers implicated the MSH2 gene in this family's cancer susceptibility. MSH2 protein expression was absent in an MSI-positive colon cancer from an affected family member. CONCLUSIONS: The inability to exclude linkage of MSH2 with the disease susceptibility, the presence of the MSI phenotype in cancers from family members sharing the same region of chromosome 2p, and the lack of immunodetectable MSH2 point to MSH2-associated HNPCC as a cause for this family's cancer susceptibility. Continued efforts to increase awareness of the heritability of endometrial cancer should improve our understanding of the disease, with resultant improved surveillance strategies, recommendations for surgical and chemoprophylaxis, and identification of patients at risk for malignancy as a result of HNPCC.

Adult↗
PubMedDate not supplied

Genomic instability on hMSH2, hMLH1, CD48 and IRF4 loci in pulmonary sarcoidosis.

Pulmonary sarcoidosis shares certain features with immune disease and neoplasia, and microsatellite DNA alterations are detectable in sputum specimens of pulmonary sarcoidosis patients. The biological basis and significance of these findings remain obscure, while information regarding the genetic basis of the disease is limited. Using multiplex PCR-based microsatellite analysis, we investigated 40 markers located on 1p, 1q, 2p, 2q, 3p, 5q, 6p, 7p, 9p, 11q, 14q and 17p in 38 sputum specimens of pulmonary sarcoidosis patients. Loss of heterozygosity (LOH) was found in 13 of 38 (34.2%) patients in at least one locus. These alterations occurred in the subset of markers located in or close to DNA mismatch repair (MMR) genes, hMSH2 (2p22.3-p16.1) and hMLH1 (3p2l.32-p21.1), as well as in CD48 (1q21-q23) and IRF4 (6p23-p25), genes associated with lymphocyte activation. Microsatellite instability (MIN) was observed in five cases (13.2%) in at least one locus. Our data suggest that genomic instability in pulmonary sarcoidosis could be due to MMR defects, while alterations of lymphocyte-specific agents could account for granuloma formation.

Adaptor Proteins, Signal Transducing↗
PubMed2001

Isolation and characterization of point mutations in mismatch repair genes that destabilize microsatellites in yeast.

The stability of simple repetitive DNA sequences (microsatellites) is a sensitive indicator of the ability of a cell to repair DNA mismatches. In a genetic screen for yeast mutants with elevated microsatellite instability, we identified strains containing point mutations in the yeast mismatch repair genes, MSH2, MSH3, MLH1, and PMS1. Some of these mutations conferred phenotypes significantly different from those of null mutations in these genes. One semidominant MSH2 mutation was identified. Finally we showed that strains heterozygous for null mutations of mismatch repair genes in diploid strains in yeast confer subtle defects in the repair of small DNA loops.

Adaptor Proteins, Signal Transducing↗